1. Field of the Invention
The present invention relates to a technology for manufacturing, for instance, a tuning fork type piezoelectric resonator using a piezoelectric substrate made of, for instance, quartz crystal or the like.
2. Description of the Related Art
The tuning fork type quartz resonator has long been adopted as a signal source for pacing of a wrist watch owing to its compactness, inexpensiveness and low power consumption, and the uses thereof are still expanding. The CI (crystal impedance) value of this quartz resonator is required to be as small as possible for the purpose of reducing the power loss, and therefore a quartz resonator of which oscillation efficiency is enhanced by forming a groove therein has been used for this purpose.
As shown in FIG. 7, the quartz resonator is provided with a pair of vibrating arms 2a and 2b in a base 1, and the grooves 31 and 32 are respectively arranged on both main surfaces of the respective vibrating arms 2a and 2b. Excitation electrodes for exciting tuning fork vibration based on bending vibration are formed in these grooves 31, 32 and the respective vibrating arms 2a, 2b. 
The above-described quartz resonator is manufactured according to the following process (refer to Patent Document 1). FIGS. 8A to 8E and FIGS. 9F to 9I are views showing the manufacturing processes of the cross sectional portion along A-A line in FIG. 7. First, after polishing and cleaning a cutout quartz wafer 10, a metal film 11 is formed by a sputtering method (FIG. 8A). A film in which gold (Au) is stacked on a backing film of, for instance, chromium (Cr) is used as the metal film 11.
Then, after applying photoresist on such a metal film 11 by a spray method for instance (FIG. 8B), the photoresist is exposed and developed in a s manner to obtain a pattern having the shape of the quartz piece 10, namely, a tuning fork shape pattern, so that a tuning fork shaped resist film 12 is formed (FIG. 8C). Thereafter, the portion of the metal film 11 not covered with the resist film 12 is removed by etching, and the whole resist film 12 remaining on the quartz wafer 10 is removed (FIG. 8D).
Next, photoresist is applied to the whole surface of the quartz wafer 10 by, for instance, a spray method, and the photoresist is exposed and developed to form a resist film 13 (FIG. 8E). Then, the resist film 13 is peeled off so that the outside shape of the quartz piece is left, and the resist film 13 at portions corresponding to the grooves 31 and 32 shown in FIG. 7 is peeled off (FIG. 9F).
Thereafter, wet etching is conducted by immersing the quartz wafer 10 in hydrofluoric acid which is an etching solution using the resist film 13 as a mask to form the outside shape of the quartz piece (FIG. 9G). 14 and 15 in FIGS. 9F to 9I are portions corresponding to the vibrating arms 2a and 2b, and 16 and 17 in FIGS. 9F to 9I are outer frame portions described for convenience of taking out a sheet of quartz piece from the quartz wafer. Then, wet etching is conducted by immersing the quartz wafer 10 in a potassium iodide (KI) solution using the resist film 13 as a mask to remove the metal film 11 at the portions corresponding to the grooves 31 and 32 shown in FIG. 7 (FIG. 9H). Then, wet etching is performed by immersing the quartz wafer 10 in hydrofluoric acid. By these processes, the grooves 31 and 32 are formed on both main surfaces of the quartz piece 10 (FIG. 9I).
Thereafter, a frequency matching process (rough adjustment in oscillation frequency) through which matching to a prescribed frequency is performed by reprocessing the side surfaces of the outside shape of the quartz piece 10 and the grooves 31, 32 by immersing the quartz wafer 10 in hydrofluoric acid. The frequency matching process includes immersing the quartz wafer 10 in hydrofluoric acid, suspending the wet etching after a predetermined period of time, cutting out a quartz piece from the original which is in a state of before forming an electrode pattern and forming the electrode on the quartz piece. A prescribed voltage is applied to the electrode and the oscillation frequency f is detected to determine whether or not the oscillation frequency f is within the predetermined frequency.
Thereafter, an electrode pattern is formed on the surface of the quartz piece 10, a fine adjustment in the oscillation frequency is conducted by shaving the metal film formed on the tip portion of the vibrating arm so as to adjust the thickness thereof.
The oscillation frequency of quartz resonator is determined depending upon the length and the width of the vibrating arms 2a and 2b, the length, width and depth of the grooves 31, 32 and the like shown in FIG. 7. Accordingly, in the frequency matching process before forming the above-described electrode pattern, since the side surfaces of the outside shape and the grooves 31, 32 of the quartz piece 10 are etched simultaneously, the change in frequency is very large, and it is difficult to suspend the etching process at the most suitable point where the predetermined frequency is obtained. Therefore, it has a problem that fine frequency adjustment doesn't go well even through the frequency adjustment process after the electrode pattern forming process, which reduces yields.
Patent Document 1    Japanese Patent Application Laid-open No. 2002-76806 (columns 0094 to 0113, FIG. 9 to FIG. 13)